When designing an internal combustion engine, it is desirable to optimize fuel economy, emissions, and durability. One means of improving fuel economy and lowering emissions may be to reduce the cylinder wall crevice volume where unburned hydrocarbons avoid combustion. The cylinder wall crevice volume is defined by the top ring land, the top compression ring, and the engine block cylinder wall. To reduce this crevice volume, the top ring land height may be decreased.
Another means of improving fuel economy may be to reduce the ring thickness which lowers engine friction. These designs expose the top ring to higher temperatures. To facilitate heat dissipation from the top ring, an internal cooling chamber disposed within the piston crown may be located adjacent the top ring groove. A coolant such as oil flowing through the chamber, transfers heat from the piston crown adjacent the top ring groove. Optimizing the shape of the chamber adjacent the top ring groove may increase stress concentrations in the ring belt that are created by combustion forces during engine operation. See FIG. 1.